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ADM706R Schematic ( PDF Datasheet ) - Analog Devices

Teilenummer ADM706R
Beschreibung +3 V/ Voltage Monitoring uP Supervisory Circuits
Hersteller Analog Devices
Logo Analog Devices Logo 




Gesamt 8 Seiten
ADM706R Datasheet, Funktion
a
+3 V, Voltage Monitoring
P Supervisory Circuits
ADM706P/R/S/T, ADM708R/S/T
FEATURES
Precision Supply-Voltage Monitor
+2.63 V (ADM706P/R, ADM708R)
+2.93 V (ADM706S, ADM708S)
+3.08 V (ADM706T, ADM708T)
100 A Quiescent Current
200 ms Reset Pulsewidth
Debounced Manual Reset Input (MR)
Independent Watchdog Timer—1.6 sec Timeout
(ADM706x)
Reset Output
Active High (ADM706P)
Active Low (ADM706R/S/T)
Both Active High and Active Low (ADM708R/S/T)
Voltage Monitor for Power-Fail or Low Battery Warning
Guaranteed RESET Valid with VCC = 1 V
Superior Upgrade for MAX706P/R/S/T, MAX708R/S/T
APPLICATIONS
Microprocessor Systems
Computers
Controllers
Intelligent Instruments
Critical P Monitoring
Automotive Systems
Battery Operated Systems
Portable Instruments
GENERAL DESCRIPTION
The ADM706P/R/S/T and the ADM708R/S/T microprocessor
supervisory circuits are suitable for monitoring either 3 V or 3.3 V
power supplies.
The ADM706P/R/S/T provide the following functions:
1. Power-supply monitoring circuitry which generates a Reset
output during power-up, power-down and brownout condi-
tions. The reset output remains operational with VCC as low
as 1 V.
2. Independent watchdog monitoring circuitry which is acti-
vated if the watchdog input has not been toggled within
1.6 seconds.
3. A 1.25 V threshold detector for power fail warning, low bat-
tery detection, or to monitor an additional power supply.
4. An active low debounced manual reset input (MR).
The ADM706R, ADM706S, ADM706T are identical except for
the reset threshold monitor levels which are 2.63 V, 2.93 V, and
3.08 V respectively. The ADM706P is identical to the ADM706R
in that the reset threshold is 2.63 V. It differs only in that it has
an active high reset output.
REV. A
Information furnished by Analog Devices is believed to be accurate and
reliable. However, no responsibility is assumed by Analog Devices for its
use, nor for any infringements of patents or other rights of third parties
which may result from its use. No license is granted by implication or
otherwise under any patent or patent rights of Analog Devices.
FUNCTIONAL BLOCK DIAGRAMS
WATCHDOG
INPUT (WDI)
WATCHDOG
TRANSITION
DETECTOR
WATCHDOG
TIMER
WATCHDOG
OUTPUT(WDO)
VCC
70A
MR
VCC
VREF*
POWER FAIL
INPUT (PFI)
1.25V
RESET &
WATCHDOG
TIMEBASE
RESET
GENERATOR
RESET,
(P = RESET)
ADM706
POWER FAIL
OUTPUT (PFO)
*VOLTAGE REFERENCE = 2.63V (P/R), 2.93V (S), 3.08V (T)
VCC
70A
MR
RESET
GENERATOR
RESET
RESET
VCC
VREF*
POWER FAIL
INPUT (PFI)
1.25V
ADM708
POWER FAIL
OUTPUT (PFO)
*VOLTAGE REFERENCE = 2.63V (R), 2.93V (S), 3.08V (T)
The ADM708R/S/T provide the same functionality as the
ADM706R/S/T and only differ in that:
1. A watchdog timer function is not available.
2. An active high reset output (RESET) in addition to the
active low (RESET) output is available.
All parts are available in 8-lead DIP and narrow SOIC packages.
One Technology Way, P.O. Box 9106, Norwood, MA 02062-9106, U.S.A.
Tel: 781/329-4700 World Wide Web Site: http://www.analog.com
Fax: 781/326-8703
© Analog Devices, Inc., 1999






ADM706R Datasheet, Funktion
ADM706P/R/S/T, ADM708R/S/T
Power-Fail Comparator
The power-fail comparator is an independent comparator which
may be used to monitor the input power supply. The compara-
tor’s inverting input is internally connected to a 1.25 V reference
voltage. The noninverting input is available at the PFI input.
This input may be used to monitor the input power supply via a
resistive divider network. When the voltage on the PFI input drops
below 1.25 V, the comparator output (PFO) goes low indicating
a power failure. For early warning of power failure the compara-
tor may be used to monitor the preregulator input simply by
choosing an appropriate resistive divider network. The PFO output
can be used to interrupt the processor so that a shutdown proce-
dure is implemented before the power is lost.
INPUT
POWER
R1
1.25V
PFO
POWER-FAIL
POWER-FAIL PFI
OUTPUT
INPUT
ADM70x
R2
Figure 5. Power-Fail Comparator
Adding Hysteresis to the Power-Fail Comparator
For increased noise immunity, hysteresis may be added to the
power-fail comparator. Since the comparator circuit is nonin-
verting, hysteresis can be added simply by connecting a resistor
between the PFO output and the PFI input as shown in Figure
6. When PFO is low, resistor R3 sinks current from the sum-
ming junction at the PFI pin. When PFO is high, resistor R3
sources current into the PFI summing junction. This results in
differing trip levels for the comparator. Further noise immunity
may be achieved by connecting a capacitor between PFI and GND.
INPUT
POWER
+3.3V
ADM663A
VCC
R1 1.25V
PFO TO P NMI
PFI
ADM70x
R2
R3
VL
=
1. 25
+
R1

1. 25
R2
VCC – 1.
R3
25

V
MID
1.
25

R1 + R2
R2

Valid RESET Below 1 V VCC
The ADM70x family of products are guaranteed to provide a
valid reset level with VCC as low as 1 V. Please refer to the Typi-
cal Performance Characteristics. As VCC drops below 1 V, the
internal transistor will not have sufficient drive to hold it ON so
the voltage on RESET will no longer be held at 0 V. A pull-
down resistor as shown in Figure 7 may be connected externally
to hold the line low if it is required.
ADM70x
RESET
GND
R1
Figure 7. RESET Valid Below 1 V
Typical Performance Characteristics
VCC
RESET
400ms/DIV
Figure 8. ADM706/ADM708 RESET Output Voltage vs.
Supply Voltage
3.3V
PFO
0V
0V
VL VH
VIN
Figure 6. Adding Hysteresis to the Power-Fail
Comparator
VH
=
1. 25
1

+

R2
R2
+
×
R3
R 3 
R1

VCC
RESET
400ms/DIV
Figure 9. RESET Output Voltage vs. Supply Voltage
–6– REV. A

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